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Abstract:

A mobile electronic device including a casing, a signal generator housed
within the casing, for generating a signal that has a frequency higher
than the human audible range, at least one speaker housed within the
casing and coupled with the signal generator, for producing analog output
from the signal generated by said signal generator, wherein the analog
output produced by the at least one speaker is (i) substantially
inaudible, and (ii) causes the casing to vibrate at a frequency
approximately equal to a resonant frequency of the casing.

Claims:

1. A mobile electronic device comprising: a casing; a signal generator
housed within said casing, for generating a signal that has a frequency
higher than the human audible range; at least one speaker housed within
said casing and coupled with said signal generator, for producing analog
output from the signal generated by said signal generator, wherein the
analog output produced by said at least one speaker is (i) substantially
inaudible, and (ii) causes said casing to vibrate at a frequency
approximately equal to a resonant frequency of said casing.

2. The mobile electronic device of claim 1 wherein the signal generated
by said signal generator is a composite of at least two harmonics, each
of which has a frequency higher than the human audible range.

3. The mobile electronic device of claim 1 wherein the at least two
harmonics each has a frequency in the range of 20-30 KHz.

4. The mobile electronic device of claim 2 wherein the difference in
frequencies for two of the at least two harmonics is approximately equal
to the resonant frequency of said casing.

5. The mobile electronic device of claim 4 wherein the difference in
frequencies for two of the at least two harmonics is in the range of
20-50 Hz.

[0002] The field of the present invention is vibrators for mobile
electronic devices.

BACKGROUND OF THE INVENTION

[0003] Many modern mobile electronic devices include speakers that
generate audible outputs, and vibrators that are enabled when the audible
outputs are not desired. A vibrator provides indications of activity,
such as incoming calls or alarms, by vibrating a mobile device. Most
common vibrators use motors with unbalanced weight on the motors'
rotating part. The vibrator produces vibrations at low frequencies, which
are sub-audible.

[0005] There is thus provided in accordance with an embodiment of the
present invention a mobile electronic device including a casing, a signal
generator housed within the casing, for generating signals, at least one
speaker housed within the casing and coupled with the signal generator,
for producing sound from a signal generated by said signal generator,
wherein the sound produced by the at least one speaker is (i)
substantially inaudible, and (ii) vibrates the casing at a frequency
approximately equal to a resonant frequency of the casing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present invention will be more fully understood and appreciated
from the following detailed description, taken in conjunction with the
drawings in which:

[0007] FIG. 1 is a simplified block diagram of a mobile device with
speakers that generate sound signals that produce inaudible vibrations of
the mobile device, in accordance with an embodiment of the present
invention; and

[0008]FIG. 2 is a simplified diagram of the speakers of FIG. 1 positioned
within a casing of the mobile device, in accordance with an embodiment of
the present invention.

[0010] Reference is now made to FIG. 1, which is a simplified block
diagram of a mobile device 100 with speakers that generate sound signals
that produce inaudible vibrations of the mobile device, in accordance
with an embodiment of the present invention. As shown in FIG. 1, mobile
device 100 includes six primary components; namely, a baseband and
application processor 110, an audio subsystem 120, a power subsystem 130,
a data storage 140, a power amplifier 150 and an antenna 160. Baseband
and application processor 110 includes a signal generator 115. Audio
subsystem 120 includes one or more speakers 125. In accordance with an
embodiment of the present invention, speakers 125 receive input digital
signals from signal generator 115, and generate output analog audio.
Power amplifier 150 includes a radio frequency (RF) interface 155.

[0011] Mobile device 100 also includes a keyboard 170 for input, a display
180 for output, and an optional subscriber identification module (SIM)
190.

[0012] Vibrations of mobile device 100 are sensed through the device's
body and casing. In this regard, reference is now made to FIG. 2, which
is a simplified diagram of speakers 125 positioned within an outer casing
101 of mobile device 100, in accordance with an embodiment of the present
invention. As shown in FIG. 2, speakers 125 are positioned within a
chamber 102 adjacent to outer casing 101.

[0013] Outer casing 101 generally has a limited frequency response,
limited to low frequencies. The frequency response of outer casing 101
generally has one or more resonant frequencies. In addition, the
frequency response of outer casing 101 is generally non-linear, and its
response to a vibration stimulus within its band pass may be modeled as
f(x)=ax+bx2+cx3+. . . , where x denotes a stimulus, and f(x)
denotes the vibration result.

[0014] Due to size constraints of mobile devices, the frequency response
of prior art speakers is generally limited to low frequencies, and the
sound pressure that the speakers generate is generally below 100 Hz is
limited.

[0015] In accordance with an embodiment of the present invention, signal
generator 115 generates a composite sound signal as a mix of two high
frequency harmonics. The composite signal is input to speakers 125, which
in turn cause mobile device 100 to vibrate at low frequencies near the
resonant frequency of outer casing 101. The sound signal generated by
signal generator 115 is represented as

S(t)=sin (2πfht)+sin (2π(fh+fr)t), (1)

where fr is approximately equal to the resonant frequency of outer
casing 101, and the frequencies fh and fh+fr are high
enough to be above the human audio range and yet within the response
range of speakers 125. Generally, selecting fh within the range of
20-30 KHz satisfies this requirement.

[0016] Due to the non-linearity of the frequency response of outer casing
101, the vibrations generated by the signal S(t) of EQ. 1 include mixed
harmonics corresponding to sums and differences of the frequencies
fh, and fh+fr. Since the frequency response of outer
casing 101 is low pass, all combinations of fh and fh+fr
are dampened, expect for the difference frequency fr, which is
passed and which generates significant vibrations of outer casing 101 due
to resonance.

[0017] According to an embodiment of the present invention, if the
resonant frequency of outer casing 101 is unknown, signal generator 115
varies the frequency fr gradually over time so as to sweep through
the relevant resonant frequency range. For example, if the resonant
frequency of outer casing 101 is estimated to be in the range of 20-50
Hz, signal generator 115 varies frequency fr over 20-50 Hz; say,

fr=fm+A sin (2πfst), (2)

where fm is the middle frequency, fm=35 Hz, A is half of the
sweep range, A=15 Hz, and fs is a sweep increment that is
significantly below the resonant frequency, say between 1-2 Hz.

[0018] In the foregoing specification, the invention has been described
with reference to specific exemplary embodiments thereof. It will,
however, be evident that various modifications and changes may be made to
the specific exemplary embodiments without departing from the broader
spirit and scope of the invention as set forth in the appended claims.
Accordingly, the specification and drawings are to be regarded in an
illustrative rather than a restrictive sense.